Chronic obstructive lung disease and obesity increase the work ofbreathing and predispose to respiratory failure. In both conditions there is a significant degree of respiratory muscle dysfunction once respiratory failure has developed, but the pathogenesis of the respiratory muscle dysfunction is poorly understood. The purposes of this project are to explore two mechanisms which affect the ability of the respiratory muscles to sustain adequate levels of ventilation. The first approach concerns the effect of protein and caloric malnutrition on the respiratory muscles. We have demonstrated that impaired nutritional status reduces the diaphragmatic muscle tissue mass and sharply curtails respiratory muscle strength and endurance. In this project we will evaluate the extent to which nutrition is poor in patients with chronic obstructive lung disease, the impact of impaired nutritional status on their respiatory muscle function, and the temporal relations between impaired nutritional status, dyspnea and respiratory failure. The second approach entails evaluation of the respiratory muscle capacity to perform ventilatory work and the magnitude of the ventilatory load. This requires independent estimates of respiratory system impedance on the one hand, and respiratory muscle strength and endurance on the other.